Detection of the state of a refrigerator door

ABSTRACT

A method is presented for inference of the position of the door of a refrigeration system by analysis of specific temperature profiles from within the controlled cavity

RELATED APPLICATIONS

This application is related to U.S. application No. 61085400 filed 31 Jul. 2008 and No. 61085823 filed 1 Aug. 2008. Applicant hereby claims priority of these applications, and the content of these applications are hereby incorporated in this application as if fully recited herein.

FIELD OF THE INVENTION

This invention relates to control of refrigerators and particularly to detecting remotely whether a refrigerator door is open or closed.

BACKGROUND OF THE INVENTION

Refrigerated containers, be they small units used in residences or large containers used for the shipping of perishable food items are designed to operate with their main access doors closed. Should these doors be open for extended periods of time, the cooling equipment is unable to keep the refrigerated cavity at the desired temperature. As a result, the refrigeration equipment continues to run for excessive periods of time, putting excessive stress on that equipment and consuming an unexpected amount of energy.

Many such pieces of equipment are equipped with door sensors, which are used to turn off the refrigeration equipment when the doors are not closed. Typically, these sensors are composed of magnets on the moveable doors and magnetic field sensitive switches, such as “reed” switches mounted on the door frames. Electrical connections through these switches cause the refrigeration equipment to be disabled so long as the doors are open. In addition, there may be a timer implemented, which energizes some sort of user notification should the door(s) be kept open for an excessive time period.

The effort of wiring such door switches can be significant in large pieces of industrial refrigeration equipment, such as truck trailers or ocean-going containers. This is exacerbated when attempting to install door switches in an after-market situation, where as much as 50 feet of wire may have to be channeled from the rear-mounted doors to the front-mounted refrigeration equipment.

SUMMARY OF EMBODIMENTS OF THE INVENTION

According to an embodiment of the invention, the status of a door is obtained by inference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a refrigeration system embodying aspects of the invention.

FIG. 2 is a schematic diagram illustrating a refrigeration system as shown in FIG. 1 and including a control and communication system embodying aspects of the invention.

FIG. 3 is a flow chart illustrating the operation of the system in FIG. 1

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1 a refrigerated container includes a refrigeration unit 1 coupled with an insulated container 2. Doors 3 on the container 2 facilitate insertion and removal of product within the container. The refrigeration unit 1 discharges cold air 4 into the container 2, while warm air 5 is returned from the container to the refrigeration unit 1 for re-cooling.

The refrigeration unit 1 is controlled by a thermostat 6. It cycles the refrigeration unit 1 ON or OFF as required to bring the temperature of the container 2 to an acceptable departure from a desired setpoint 7. Temperature feedback is provided by any combination of remote temperature probes 8 in the container 2 and return temperature of the warm air 5.

If the refrigerated container 2 is closed, the system will be satisfied (i.e. container temperature measured at the probe or probes 8 is close to setpoint 7 within some time period. Then the refrigeration unit will cycle ON and OFF as required to maintain this temperature. Should the doors 3 be left open, the refrigeration unit 1 will run continuously, since the constant influx of warm outside ambient air prevents the refrigeration unit 1 from ever getting the container 2 to the proper temperature.

In one embodiment, the refrigerated system is continuously monitored by a local computer which in turn is connected wireles sly to an Information Technology system. This is illustrated in FIG. 2. Here, the refrigerated container 2 and refrigeration unit 1 are as described in FIG. 1. Integral to the Refrigeration Unit 1 is a computer or controller 13, which correctly operates the refrigeration machinery as appropriate to the various sensors throughout the system. This controller 13 is continuously monitored by a second computer labeled Monitor 14. Should the Monitor 14 determine that a change in door state has occurred, it can communicate over a wireless link 16 to a Network Operations Center (NOC) 15. This wireless link may be any of a local RF network, cellphone, satellite, etc.

The NOC 5 alerts a user to the change of state by any of several modalities including a website display 17, pager 18 or cellphone text message 19.

The system determines that the doors have been left open by monitoring the time it takes the refrigeration unit to bring the container to the correct temperature. If the time exceeds a threshold value, it indicates that the doors 3 have been left open. If, following a door open state the container temperature once again cools down close to the set point, this indicates that the doors have once again been closed.

According to an embodiment the monitoring is done by the refrigeration controller 13 itself rather than by a separate monitoring device 14 as described above.

FIG. 3 is a flowchart illustrating the operation. Here, for simplicity, “=” has been used to indicate an approximate equality within acceptable bounds. The system follows steps 31 to 38.

According to one embodiment of the invention, the steps 31 to 38 are performed by the controller 13. According to another embodiment, the steps 31 to 38 are performed by the monitor 14. According to yet another embodiment, the steps 31 to 38 are performed by a combination of monitor 14 and controller 13. For simplicity, the following description refers to the controller/monitor 13/14, but it will be understood that the description applies equally to the embodiments involving the controller 13 alone, the monitor 14 alone, and to the controller 13 combined with the monitor 14.

In step 31 the controller/monitor 13/14 determines whether the refrigeration unit is on by sensing whether a discharge 4 exits out of the refrigeration unit 1. If the refrigeration unit is off, the controller/monitor 13/14 continues sensing for the discharge. In one embodiment, the controller/monitor 13/14 sends a signal 16 to the Network Operations Center (NOC) 15 informing the center 15 that no discharge 4 exits out of the refrigeration unit 1 and that the refrigeration unit 1 is off.

If the response to in step 31 is yes, that is if the refrigeration unit is on, the controller/monitor 13/14 proceeds to step 32. The controller/monitor 13/14 regulates the defrosting operation of the refrigeration unit. Thus in step 32, the controller/monitor 13/14 interrogates its internal operation to indicate whether the container 2 is defrosting. If yes, the defrosting operation continues and the controller/monitor 13/14 issues as signal over the wireless link 16 to the Network Operations Center (NOC) 15 that the refrigeration container 2 is defrosting.

If the output at step 32 is no, the refrigerated container 2 is not defrosting, the controller/monitor 13/14, in step 33, compares the temperature at the temperature probe or probes 8 with the setpoint 7, or setpoint temperature at the thermostat 6, to see if they are equal within a given range. If not, this indicates that the temperature is necessarily higher than the setpoint 7 by an amount greater that the range of equality. Then, in step 34, the controller/monitor 13/14 compares the temperature at the temperature probe 8 with the setpoint 7 temperature at the thermostat 6 for a given period, such as three minutes, to determine if the temperature at the temperature probe or probes 8 remains higher than the setpoint 7 for the give period, e.g. three minutes. If not, the controller/monitor 13/14 continues comparing the temperature at the temperature probe 8 with the setpoint 7. According to one embodiment, if the output of step 34 is NO, the controller/monitor 13/14 returns to the input of step 33. According to another embodiment, the controller/monitor 13/14 sends a signal to the NOC 15 to the effect that the temperature is greater than the setpoint 7 but not for more than the given time e.g. 3 minutes.

If the output of step 34 is yes, the temperature exceeds the setpoint for more than 3 minutes, the system proceeds to step 35, to indicate that the door or doors 3 are open. The controller/monitor 13/14 then sends a signal indicating an open door to the NOC 15. The system then returns to step 31.

If the output at step 33 is yes, namely that the temperature is effectively equal to the setpoint 7 the controller/monitor 13/14 proceeds to step 36 as well as step 38. In step 36 the system determines whether the temperature at sensor 8 is equal to the setpoint 7, within the limits set, for a predetermined period such as five minutes. If no, the operation returns to step 31. If yes, this indicates that the door or doors 3 are closed. The controller/monitor 13/14 then sends a door closed signal to NOC 15. The procedure returns to step 31.

In step 38, the controller/monitor 13/14 responds to the YES at step 33 to send a signal to NOC 15 to indicate that the temperature at sensor 8 is within prescribed limits equal to the setpoint 7. This is a way of indicating that although the temperature may not have equaled the setpoint 7 for the prescribed time, e.g. five minutes, the temperature has descended to the proper range.

According to an embodiment a signal indicating open doors when the system should be cooling sets off an alarm to inform personnel to close the doors. According to another embodiment, a feedback arrangement closes the doors when the system should be cooling.

The embodiments infer the position of the door of a refrigeration system by analysis of specific temperature profiles from within the controlled cavity or container. The embodiments use inference of door status without the need for physical switches or wiring. The embodiments infer that the doors have been left open by monitoring the time it takes the refrigeration unit to bring the container to the correct temperature. If it exceeds a threshold value, it is inferred that the doors have been left open. If, following a door open state the container temperature once again cools down close to the setpoint 7, it is inferred that the doors have once again been closed.

While embodiments have been described in detail it will be recognized that the invention can be embodied otherwise without departing from its spirit and scope 

1. A method of determining the condition of a door of a refrigerated chamber, comprising: sensing the temperature of a refrigerated chamber having a door; analyzing the temperature profile of the sensed temperature; inferring from the temperature profile the status of the door.
 2. A refrigeration system, comprising: a refrigeration chamber; a door closing said chamber; a temperature sensor in the chamber; a temperature-profile sensing controller connected to said temperature sensor and otherwise separate from the door. 